The present invention relates to nondispersive infrared gas analyzers; and more particularly, the invention relates to radiation receivers and detectors for such analyzers.
Analyzers of the type to which the invention pertains use basically the principle of selective absorption. Broadband infrared radiation is selectively absorbed by the gas component to be detected in, and as part of, a sample gas; and the residual radiation of these wavelengths and band or bands is detected by means of detection chambers being filled with just that particular component. A problem arises when the sample gas contains also another gas or gases whose absorption band or bands overlap any absorption band of the component of interest. These interfering components falsify the measuring result; and the error is, of course, the greater, the larger the overlap and the higher the concentration of that interfering component. The problem has been dealt with in various ways.
A particular method and apparatus for measuring the concentration of particular components in a carrier gas has been described, for example, in U.S. Pat. Nos. 3,162,761 and 2,951,939. Particularly, the latter patent includes a suggestion to provide a special filter being strata of gases of the type that produces the interference problem. This particular filter removes the overlapping band portions from the analysis. U.S. Pat. No. 3,925,667 suggests another approach and U.S. Pat. Nos. 3,725,702 and 4,156,812 deal with null-point shifts generally.